Stripe formation: A quantum critical point for cuprate superconductors

We discuss the effects of a quantum critical point located nearby optimum doping and related to local charge segregation (stripe phase). The fluctuations in the critical region produce at the same time a strong pairing mechanism and a non-Fermi liquid behavior in the normal phase above the superconducting critical temperature. Superconductivity is a stabilizing mechanism against charge ordering, i.e. the incommensurate charge density wave quantum critical point is unstable with respect to superconductivity. A complete scenario for the cuprates is presented.Comment: Proceedings of the Cape Cod Conference on "Spectroscopies in Novel Superconductors, SNS 97", to appear on J. Phys. and Chem. of Solid

PHASE-SEPARATION AND SUPERCONDUCTIVITY IN THE KONDO-LIKE SPIN-HOLE COUPLED MODEL RID C-6309-2009 RID C-7176-2009

We have investigated the presence of a phase separation in the phase diagram of a Kondo-like spin-hole coupled model. Within a mean-field analysis we find that the system in the normal phase separates into a spin liquid and a Fermi liquid phase. The introduction of a superconducting order parameter stabilizes the system strongly reducing the phase separation region. A reasonable behaviour of T(c) vs. doping delta is also obtained

Enhancement of the spin susceptibility in disordered interacting electrons and the metal-insulator transition

The response of a disordered interacting electron gas to a time and spatially varying magnetic field is discussed. Local spin conservation leads to a generalized Ward identity, which together with global spin conservation implies that the dynamic magnetic susceptibility (q,) must obey a simple diffusive form. The same identity, when combined with the general perturbative structure of (q,), also relates the renormalization of static susceptibility st and the spin diffusion constant Ds to the renormalization of the charge diffusion constant and the Fermi-liquid interaction amplitudes. These relations are shown to be consistent with perturbations to first order in t {=1/[(2)2N0D]} but only after nontrivial cancellations. Thus the Ward identity allows both easy derivation of (q,) from the renormalized theory and a consistency check on the scaling equations. By using the renormalization-group equations for these parameters, it is shown that there is strong enhancement of st and decrease in Ds with lowering temperature. The significance of this with respect to the metal-insulator transition is discussed. \ua9 1986 The American Physical Society